Count element frequencies

How to count the frequencies of elements in a list?

• Convert to a dictionary with key is the element, value is the frequency
• Sort the dictionary

Solution 1

First construct a list with repetitive elements:

data_freq = [randint(0,10) for _ in range(30)]

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{% asset_img 'data_freq.PNG' %}

res = {}

for ele in data_freq:
    if ele in res:
        res[ele] += 1
    else:
        res[ele] = 1

res = dict(sorted(res.items(), key=lambda x: x[1], reverse=True))

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Solution 2

Construct a dictionary based on the data, initial values are 0

res2 = dict.fromkeys(data_freq, 0)

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{% asset_img 'fromkey.PNG' %}

Construct the count dictionary

for d in data_freq:
    res2[d] += 1

res = dict(sorted(res.items(), key=lambda x:x[1], reverse=True))

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To select the top 3, can use heapq

import heapq

heapq.nlargetst(3, ((v,k) for k,v in d.items())

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Counter

It’s very easy to do this with Counter from collections.

from collections import Counter

Counter(data_freq)

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Use most_common method

c = Counter(data_freq)
c.most_common()

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An example of word count

Read a file containing zen of python and perform a word count.

Use RegEx to split words

import re
wl = re.split('\W+', zen)
wc = Counter(wl)
wc.most_common(3)

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